We have investigated the temperature dependence of magnetic dynamics in a spinel-type vanadium oxide MnVO by inelastic neutron scattering. The scattering intensity of excitation around 20 meV disappears in the collinear intermediate-temperature cubic-ferrimagnetic phase, which reveals that this excitation should be peculiar to the orbital ordered phase. We have found a weakly dispersive mode emergent from a non-integer wavevector at 56 K, which lies in the cubic-ferrimagnetic phase between non-coplanar ferrimagnetic and paramagnetic phases. This indicates that the probable presence of an incommensurate instability in the simple collinear structure.

We investigate the magnetic dynamics in the spinel-type vanadium oxide MnVO. Inelastic neutron scattering around 10 meV and a Heisenberg model analysis have revealed that V spin-wave modes exist at a lower-energy region than previously reported. The scattering around 20 meV cannot be reproduced with the spin-wave analysis. We propose that this scattering could originate from the spin-orbital coupled excitation. This scattering is most likely attributable to V spin-wave modes, entangled with the orbital hybridization between orbitals.

The magnetic structure and magnetoelectric effect have been investigated for single crystals of the antiferromagnet CoNbO. Single-crystal neutron diffraction and magnetic susceptibility measurement have revealed that the magnetic structure is different from a collinear arrangement with spin parallel to the trigonal axis as proposed previously. Co magnetic moments are found to be almost lying in the basal plane, which lowers the magnetic symmetry to with the propagation vector = 0. Associated with the magnetic phase transition, a sharp anomaly in the dielectric constant and displacement current indicate the appearance of the magnetoelectric below Neel temperature TN with a large coupling constant up to 30 ps/m. The existence of off-diagonal components in a magnetoelectric tensor indicate the formation of ferrotoroidic order in CoNbO. Such a magnetoelectric effect can be ascribed to the reduction of symmetry caused by simple antiferromagnetic order in a honeycomb network.

The half-filled topmost valence band of Ir in several iridates such as SrIrO, IrO, and CaIrO has been proposed to originate mainly from the spin-orbit coupled states. In pyrochlore iridates IrO (: rare earth), some exotic electronic states are theoretically proposed by assuming states. However, the octahedral coordination around Ir is trigonally distorted, which may affect the energy level scheme of Ir states. Here, we report spectra of resonant elastic and inelastic X-ray scattering in EuIrO at the Ir edges. A large suppression of the magnetic scattering signal at the Ir edge supports the picture rather than the one. The inelastic scattering spectrum indicates that the magnitude of the trigonal field on the Ir states is evaluated to be comparable to the spin-orbit interaction. The energy diagram of the state is proposed based on the simple cluster model.

The phonon dynamics of spin-state crossover for perovskite LaCoO was investigated using infrared and inelastic X-ray spectroscopy. We observed that the Co-O bond stretching phonons couples to the thermally excited spin-state. The momentum dispersion of the optical mode is anomalously dispersionless (less than 3 meV), and this supports the spin-state disproportionation scenario. The steep enhancement of spin-state fluctuation compared to the charge gap suggests the density dependent spin state disproportionation; a simple low spin (LS)/high spin (HS)- or LS/intermediate spin (IS)-state disproportionation is realized at the initial stage with dilute HS- (or IS-) state density, while the complex spin-state disproportionation involving all of the LS-, IS- and HS-state is formed when the density of HS- (or IS-) state is enhanced.

Infrared optical and inelastic X-ray scattering spectra have been systematically investigated in combination with first-principles calculations for paraelectric and antiferromagnetic perovskite SrBaMnO single crystals, which are close to a ferroelectric transition arising from off-center displacement of magnetic Mn ions. One optical phonon rapidly softens toward zero frequency at room temperature with increasing . This soft-mode behavior is also reproduced by the first-principles calculations, from which we have predicted the vibration mode of all the optical phonons. Below the antiferromagnetic-transition temperature, the soft mode hardens with decreasing temperature and then resoftens toward the lowest temperature.

Perovskite-type manganites exhibit various interesting phenomena arising from complex interplay among spin, charge, orbital, and lattice degrees of freedom. As the respective examples, perovskite-type YMnO and SrBaMnO are discussed. In the YMnO, the ferroelectric lattice distortion associated with the -type spin order is observed for the first time. Displacement-type ferroelectricity with off-center magnetic ions is discovered for SrBaMnO, which shows both large polarization value and strong coupling between ferroelectricity and magnetism.

Magnetic and magnetoelectric (ME) properties have been studied for single crystals of Sc-doped -type barium hexaferrites. Magnetization () and neutron diffraction measurements revealed that by tuning Sc concentration a longitudinal conical state is stabilized up to above room temperatures. ME measurements have shown that a transverse magnetic field () can induce electric polarization () at lower temperatures and that the spin helicity is nonvolatile and endurable up to near the conical magnetic transition temperature.

We have investigated the spin/orbital phase diagram in the perovskite orthovanadate VO ( = Eu, Y, Dy, and Ho) by measurements of magnetization, dielectric constant, specific heat, Raman scattering spectra, and X-ray diffraction, focusing on the interplay between the V spin and the moment of the ion. The results cannot be uniquely explained in terms of the exchange interaction between the V spin and the -ion moment. By comparing this phase diagram with the spin/orbital ordering in TbVO, it is evident that the critical competition between the C-type spin/G-type orbital ordered phase and the G-type spin/C-type orbital ordered one depends not only on the GdFeO-type lattice distortion but also on the presence of the moment of the ion. The magnetic field induced phase transition of the spin/orbital ordering is achieved concomitantly with polarizing moments for DyVO and HoVO. The results cannot be uniquely explained in terms of the exchange interaction between the V spin and the -ion moment. The coupling of the moment polarization with the lattice distortion tied with the orbital ordering of the V sublattice may also be relevant to this field induced phase transition.

We discovered a reversible electric polarization flop from the axis () to the axis () in multiferroic TmMnO below 5 K by applying a magnetic field of approximately 0.5 T along the axis. This phenomenon is the first example of the rare-earth () compound MnO. This magnetic-field-induced polarization flop corresponds to a magnetic phase transition from one incommensurate magnetic (ICM) phase to another ICM phase, which is equivalent to an ICM phase above 5 K under no magnetic field. The spin chirality in the plane, which was observed in the phase by polarized neutron diffraction, disappeared in the ICM phase. This indicates that the polarization in the ICM phases of TmMnO was induced by an type interaction.

TbMnO exhibits a spontaneous electric polarization along concomitantly with a spiral spin ordering modulated along below = 28 K. We have performed inelastic X-ray scattering measurements on a single crystal of TbMnO to clarify whether phonon anomalies related to the ferroelectricity exist. We measured transverse modes, especially the Mn-O-Mn bending mode polarized along and propagating along , which we expect is most relevant to the ferroelectricity. However, no anomaly was found in the phonon dispersion below 50 meV across . The present result suggests that the mechanism of ferroelectricity in TbMnO is different from that of a conventional displacive-type ferroelectric. The weak coupling between electric polarization and lattice in TbMnO strongly suggests that the ferroelectricity is mainly derived from the spiral spin ordering.

An inelastic X-ray scattering study on a single crystal of TbMnO was performed to reveal whether phonon anomaly related to the appearance of the ferroelectricity exists. We have measured the transverse modes, especially the Mn-O-Mn bending mode, polarized along the axis propagating along the axis, because these modes are expected to be most relevant to the spontaneous electric polarization along the axis concomitantly with the spiral spin ordering modulated along the axis. However, no anomaly in phonon dispersions was observed even below the ferroelectric transition temperature below 50 meV. The present result suggests that the mechanism of ferroelectric transition in MnO is different from that of a conventional displacive-type ferroelectric.

The discovery of magnetoelectric (ME) effects caused by a cycloidal spin order has initiated an intense research on new class of ME materials. Among them one interesting class of materials is the hexaferrites such as Y-type (AMeFeO: Me=transition metal), M-type (AFeO: A=Pb, Ca, Sr, Ba, etc.), where types of elementary blocks and their stacking order are different. These materials show a variety of complex magnetic ordering. In this presentation recent neutron diffraction experiments on multiferroic hexaferrites performed at the JRR-3 Neutron Science Facility of Japan Atomic Energy Agency (JAEA) are reported.

We aim at constructing a polarisation analysis neutron spectrometer at Materials and Life Science Experimental Facility (MLF) of Japan Proton Accelerator Research Complex (J-PARC) based on a collaboration of KEK and Tohoku Univ. The proposed instrument, named POLANO, is designed as a compact chopper spectrometer with a rotary detector bank ( = 17.5 m, = 2.5 m). At the first phase of the project, we will concentrate the 30 meV region using a fan type bender supermirror spin analyser because rich scientific targets in basic and application materials science exist in this region. In the second phase, we will try to install a He spin filter analyser for the 100 meV region. This project passed in the final board of J-PARC on SEP-2011, and the construction has been authorized already.